In shooting sports, high-performance low-cost ammunition is highly desirable. High performance can mean, for example, high accuracy at long ranges. Traditionally, center fire cartridges provide such performance, but, they are relatively expensive. Rimfire cartridges have provided inexpensive cartridges with reasonable performance. In recent years, the .17 Horady Magnum Rimfire (.17 HMR) cartridge has become very popular in applications such as varmint hunting. This cartridge produces an extremely high muzzle velocity (e.g., twice the speed of sound), much higher than conventional rimfire cartridges. This high muzzle velocity combined with the relatively low wind resistance of the .17 projectile combine to minimize bullet drop and produce a relatively flat trajectory thus offering the high performance of center fire cartridges at a rimfire price. Rifles that chamber the .17 HMR are commercially available, for example, from Savage Arms, Marlin Firearms and Sturm, Ruger & Company. Such inexpensive high performance cartridges are conducive to high volume firing, especially since a semiautomatic rifle, the model A17, that accepts such cartridges is now available from Savage Arms. The A17, and other rimfire rifles, particularly semiautomatic rimfire rifles, utilize a rotary magazine that fits within a magazine receptacle in such rifles and is within the form factor of the rifles. That is, the exposed surface of the magazine follows the contours of the rifle. Low-cost high capacity magazines are known that plug into the receptacle for the rotary magazines for 22 caliber rimfire cartridges. Improvements to such high capacity magazines to accommodate the larger and higher powered .17 HMR cartridges would be well received.